In the commercial food processing industry, it is conventional to utilize conveyors having a series of grids attached to the conveyor to carry the food product over a predetermined path for processing. For example, in the baking industry, large proofers and ovens employ continuously moving conveyors to transport dough products through the baking process. The conveyors trace a multi-tier spiral or circular path through the proofers or ovens to achieve sufficient residence time to allow the dough to rise in the proofer and to bake in the oven. The dough products are placed on metal pans which can vary in size and shape depending on the product, i.e. rolls, loaves, etc. One particularly successful bakery conveyor system has been developed by APV Baker, and is generally disclosed in a number of prior patents including U.S. Pat. Nos. 4,997,365 and 5,010,808.
Generally, bakery conveyors include an elongated track supporting and guiding a conveyor chain to define a path of travel. A series of grids, attached to the chain, support a series of pans carried along the path through one or more processing operations. It is inevitable that pans will be jostled around on the track due to such things as vibration or interference with other structures or pans. Travel around curves in oval or spiral conveyors will also cause the pans to move and change position on the grid. Shifting of any significant amount is undesirable because it can cause interference between pans, and occasionally cause pans to fall off the conveyor or otherwise cause a jam, which results in downtime of the conveyor and the baking system.
Magnetic grids, usually containing 2 or more magnets per grid, have been suggested to hold the pans in place. In some designs, the magnets are fixed vertically but allow a limited amount of movement in a horizontal plane. In other designs as exemplified by Kasik U.S. Pat. No. 4,836,360, the magnets can move vertically and horizontally. Magnetic grids are generally characterized by the fact that the pans are supported on and carried by the magnets and the magnets in turn carried by the grids. In effect the magnets, not the grids, provide the support surface for the pans.
Since not all track is straight, travel of the pans around curves can create problems. Sometimes pans are placed on only a single grid, while at other times a pan will be supported on 2 or more grids. In traversing curves, relative movement between the pans and the grids is a given, and controlled magnet movement has been suggested as a mechanism for allowing this movement around curves yet keeping the pans affixed to the magnets. Pans originally misaligned will at best remain misaligned, and at worst become further misaligned, interfere with another pan, or fall off the conveyor. Due in part to the various combinations of pan size and grid geometry, problems can arise which are not all readily solved. For example, baking can be disrupted if a pan is not placed properly, or if it interferes with another pan.
Centerguides have also been used to help align pans in the first instance, and keep them tracking correctly, including tracking through curves. Centerguides are mechanical structures which project above the grid surface to engage or contact some part of the underside of a pan which is being carried on the surface of a conventional grid or on the magnets of a magnetic grid. Conventional mechanical centerguides utilize a guide member which projects above the grid and engages the underside of the pan intermediate a pair of dough-holding pockets; mechanical engagement between the guide and the pockets tends to keep the pan tracking correctly. Mechanical centerguides are sometimes preferred to magnetic grids because they function to keep the pan oriented with respect to the direction of conveyor travel. Theoretically the center of the pan, which is engaged by the centerguide, is held on the center of conveyor travel. However pans vary, for example in number of pockets, placement of pockets, location of the inter-pocket gaps, etc., presenting limits to the utility of centerguides in some circumstances. The situation can be further complicated when pans of different configuration are utilized by the baker at the same time, such that successive grids are carrying pans of different configuration.
To overcome some of these problems, a rocker type guide has been employed. The rocker guide has two physically connected but laterally spaced guides, one of which is centered on the path of travel, the other being non-centered, and only one of which is operative at any given time. The guides are mounted on opposite ends of the rocker which can pivot to dispose one of the guides below, and the other guide above the grid surface. The pan underside pushes one of the guides below the grid to raise the opposite guide hopefully between adjacent pockets of the pan. As the conveyor carries the grids around the defined track, the guide, riding in the space between the pockets, attempts to maintain the orientation of the pan on the grid. Even with rocker guides, the operative guide is held above the grid surface by a positive mechanical mechanism.
Unfortunately, the width of the rocker guides vary with different grids, dictated by the type of product being processed. In some situations, the width of the rocker guide is insufficient and both of the laterally spaced guides may lie beneath the bottoms of two pockets, rather than in between pockets. This condition would fail to laterally restrict the pans and indeed would cause instability in the pans. Further, neither of the two aforementioned guides seek to accommodate different depths of the pockets, or differently sized spaces between the pockets.
There is a large installed base of conveyor systems with grids of various types which might be improved by use of a magnetic centerguide according to the present invention. The economies of bringing the invention to such environments would be significantly enhanced if a centerguide structure capable of retrofitting, and a method of retrofitting existing grids with a centerguide, could be provided.